Cell-based wireless communications provide voice, data and messaging to millions of people. A cell system typically divides a geographic area into cells. A base station operating in the cell receives communications from mobile devices and routes those communications to the appropriate destination. The destination may be within the cell, within another cell, or on another network.
A major limitation in cellular and PCS wireless telephone networks is co-channel interference. In the case of TDMA networks, such as GSM, the co-channel interference arises from the reuse of the spectrum allocation to provide the communications services. A signal may contain not only the desired forward channel from the current cell, but also signals originating in more distant cells. If the interference from a distant cell causes a degradation of the ability of the handset to receive correctly the desired signal, it becomes important to identify the source of co-channel interference and measure the relative strength of interference relative to the desired signal. More information about co-channel interference and its detection may be found in commonly owned U.S. Pat. No. 7,013,113 issued Mar. 14, 2006 for a “Method and Apparatus for Co-Channel Measurements and Interference Component Separation Based on Statistical Signal Processing in Drive-Test Area,” U.S. Patent Application Publication 2007/0207740 published Sep. 6, 2007 for “Use Of SCH Bursts For Co-Channel Interference Measurements,” and United States Patent Application Publication 2009/0215443 published Aug. 27, 2009 for a “Cellular Drive Test System Network.”
The U.S. Pat. No. 7,013,113 and the 2007/0207740 and 2009/0215443 publications are incorporated by reference herein in their entireties for all purposes.
To improve the coverage of cellular communications, particularly within structures or high traffic areas, at least some of the functions of the base station have been incorporated into small capacity devices that serve a limited area and a limited number of calls. For example, picocells and femtocells have been developed to provide coverage within a structure (for example, a building, a train station, an airport, an apartment complex and a stadium). Deployment of one or more of these small capacity devices (generally referred to herein as a “mini-cells”) improves coverage and increases data capacity.
Mini-cells are also susceptible to interference. A system of mini-cells must be managed to assure that the cells are operating optimally and that services are provided with minimal errors and lost data.
Because most of the new cells will be deployed indoors, existing techniques of drive-test measurements are not practical. Additionally the cells, in many cases, will be purchased and installed by consumers and small business owners and not by service providers. Accordingly, the providers will not be able to configure the newly installed cells, since they may not even know their locations. Further, the sheer number of the expected deployment of mini-cells and their unpredictable behavior (being turned on and off without notice, for example) make the task of centralized and static network optimization infeasible.
New wireless cellular standards, such as IEEE 802.16m, reflect an understanding of the unique issues affecting mini-cells. These standards generally require wireless networks to include self configuration and dynamic self optimization capabilities. In turn, the manufacturers of base stations provide a so-called “sniffing” feature where a base station is able to listen to the signals of adjacent base stations in order to adjust its own parameters or, alternately, adjust the parameters of other stations in such a way as to minimize mutual interference between stations.
The “sniffing” technique may be inadequate, however, when interfering signals are weak and cannot be decoded and identified. Although methods exist for co-channel interference measurements, they are not easily applied to the self-configurable dynamic and indoor networks, since they are based on conducting drive test-based measurement campaigns.